Metal vacuum bottles comprising an inner shell, an outer shell, and a cup-shaped member mounted on the bottom portion of the outer shell to cover and protect a soldering portion of a capillary tube on the bottom portion of the outer shell are known in the prior art. The bottle has a contact welded surface between the upper end portion in the outer shell and the throat portion of the inner shell to form a space between the outer shell and the inner shell. To make the space between the shells a vacuum, air in the space is removed by conventional means, such as a vacuum pump, through a capillary tube, which is attached on the middle part of the bottom in the outer shell.
Accordingly, since the contact welded surface between the shells is typically made of a metal such as stainless steel, this surface acts as a heat transfer surface in a conventional vacuum bottle and the temperatures of contents such as boiling water, are not maintained. For example, thermal conductivity of synthetic rubber is 0.11 Kcal/m.hr..degree.C. and that of stainless steel is 24.5 Kcal/m.hr..degree.C. Thus, stainless steel conducts 223 times more heat than synthetic rubber for a given time period.
In addition, the forming and production of metal, particularly stainless steel, parts is more complicated and expensive than for rubber parts.
Stopper caps for vacuum bottles are also known in the art. In one commonly employed stopper cap, the stopper cap is provided with a thread screw that fits cooperatingly with a thread screw on the interior of the bottle throat and a rubber ring. This system is based on the principle that liquid in the bottle can be contained by threading the stopper cap into the bottle throat and sealing the connection with the rubber ring. However, with use the ring may deform or actually be separated, so as to cause an imperfect seal. Accordingly, a perfect seal is difficult, and the temperature of the contents will not be maintained.